Exciting developments are occurring in solar PV (photovoltaic) power generation. New technologies are improving manufacturing processes. Thin-film and organic (plastic) films promise to reduce PV power cost. Solar “grid-parity,” the time when solar power will cost the same as fossil fuel power, is coming soon.
PV refers to devices that turn sunlight into electricity. In a previous post, I discussed generation by solar thermal (Solar Thermal: The Other Solar Energy). Both schemes have advantages and disadvantages.
PV can turn solar energy into electricity that can supply households and industry without using any moving parts. Since mechanical devices are less reliable than electronic, these systems are nearly maintenance free. Solar Thermal requires a heat engine, such as a steam engine, and an electrical mechanical generator to produce electricity.
While PV works best with direct sun light, it will work with overcast and even fog. The greatest disadvantage of PV is that it can only deliver power in the daytime. Storage of electricity on the grid is expensive. Solar Thermal can store heat in an insulated vault and convert it to electricity when needed, but it must have direct sunlight to function since it focuses or directs (concentrates) light rays onto heat collectors. Eventually, the smart grid will be able to store energy in idle electric car batteries.
Solar Thermal technology is based on optics that were well understood by Archimedes and electric generator principles developed over a hundred year ago. Most of the advances in Solar Thermal are development in material science, engineering and instrument and control technology.
PV is the fastest growing renewable energy source. The amount of energy produced by PV doubles every two years.
Most of the advances in PV technology are the result of advances in Solid State Physics, a vanguard technology that has produced the explosion in PCs and handheld IT devices in the last 30 years.
PV panels are constructed by connecting an array of cells. Each cell consists of at least two layers or “junctions” that forms a diode. A diode is an electronic device that conducts electricity only in one direction.
Sunlight transfers its energy to electrons in the first junction thus raising them to a voltage and causing them to flow (current) to the final junction. This is the reverse of an LED (Light Emitting Diode). Here electrons (current) driven by an applied voltage transfer their energy to light as they flow from the first to the last junction.
PV progress can be measured mainly in initial cost of capital investment in solar panels. Usually, this is measured in Watts per dollars (USD). Currently, cost is about 1-Watt/$1.00, but recent research is quoting 1-Watt/$0.93. Progress is fast.
Progress in PV has mainly centered on the materials to make the junctions and manufacturing techniques. Most junctions are made of silicon; the same stuff in your computer’s chips. Other materials such as cadmium telluride (CdTe), copper-indium-gallium and selenide (CIGS), and organic polymers (plastics) are showing great promise in labs.
Originally, PV cells were manufacture one-by-one. The ideal manufacturing process would be a “role-to-role” or a process like printing wallpaper. The final product would consist of sheets that could be glued onto panels and electrically connected at the ends.
Yang Yang, a UCLA professor, heads a research solution for such a role-to-role process using CIGS thin-film technology. Another research solution, according to Russell Gaudiana, VP of research at Konarka Technology, is to print organic PV coating on a substrate in a role-to-role process.
PV technology is advancing quickly. We should see solar grid-parity in a few years. Certainly when cap and trade kicks in fossil fuels will have trouble keeping up.
Photo Credit: Konarka Technology Inc.